*>EPA
United States
Environmental Protection
Agency
EPA Protocol for the
Third Review of Existing National Primary
Drinking Water Regulations
-------
Office of Water (4607M)
EPA 810-R-16-007
December 2016
www. epa. gov/ safewater
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Table of Contents
Abbreviations and Acronyms iii
Executive Summary 1
1 Introduction 1-1
1.1 Basic Principles 1-1
1.2 Scope of Review 1-2
1.3 Organization and Contents of this Document 1-6
2 Overview of the Six-Year Review Protocol 2-1
2.1 Protocol Clarifications for the Six-Year Review 3 2-2
2.2 Elements of the Six-Year Review 3 Decision Tree 2-2
3 Detailed Discussion of Decision Tree Implementing the Protocol 3-1
3.1 Initial Review Branch 3-1
3.1.1 Inputs to the Initi al Revi ew 3-1
3.1.2 Output of Initi al Revi ew 3-3
3.2 Health Effects and MCLG Branch 3-3
3.2.1 Inputs to Health Effects and MCLG Review 3-4
3.2.2 Outputs from Health Effects and MCLG Review 3-6
3.3 Maximum Contaminant Level Branches 3-7
3.3.1 Inputs to Maximum Contaminant Level Review 3-9
3.3.2 Outputs from Maximum Contaminant Level Review 3-10
3.4 Treatment Technique Branch 3-10
3.4.1 Inputs to Treatment Technique Review 3-12
3.4.2 Outputs from Treatment Technique Review 3-12
3.5 Treatment Technique Analysis Branch 3-12
3.5.1 Inputs to Treatment Technique Analysis Review 3-12
3.5.2 Outputs from Treatment Technique Analysis Review 3-13
3.6 Methods Branch 3-13
3.6.1 Inputs to Methods Review 3-15
3.6.2 Output from Methods Review 3-16
3.7 Occurrence Branch 3-16
3.7.1 Inputs to Occurrence Review 3-17
3.7.2 Output from Occurrence Review 3-18
3.8 Treatment Branch 3-18
3.8.1 Inputs to Treatment Review 3-20
3.8.2 Output of Treatment Review 3-20
3.9 Risk-Balancing Branch 3-20
3.9.1 Inputs to Risk-Balancing Branch 3-20
3.9.2 Outputs from Risk-Balancing Branch 3-21
3.10 Implementation Branch 3-21
3.10.1 Inputs to Implementation Review 3-22
3.10.2 Outputs from Implementation Review 3-22
4 References 4-1
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Table of Exhibits
Exhibit 1.1 NPDWRs Included in the Six-Year Review 3 1-3
Exhibit 2.1 Process for Identifying NPDWRs that are Candidates for Revision 2-4
Exhibit 3.1 Initial Review Branch 3-2
Exhibit 3.2 Health Effects and MCLG Branch 3-4
Exhibit 3.3a Maximum Contaminant Level Branch 1 (Potential for MCLG Revision) 3-8
Exhibit 3.3b Maximum Contaminant Level Branch 2 (No Potential for MCLG Revision) 3-9
Exhibit 3.4 Treatment Technique Branch 3-11
Exhibit 3.5 Treatment Technique Analysis Branch 3-13
Exhibit 3.6 Methods Branch 3-14
Exhibit 3.7 Occurrence Branch 3-17
Exhibit 3.8 Treatment Branch 3-19
Exhibit 3.9 Risk-Balancing Branch 3-21
Exhibit 3.10 Implementation Branch 3-22
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
BAT
DBP
D/DBPR
EPA
EQL
HAA5
HEA
HSDB
I ARC
ICR
IRIS
MCL
MCLG
MDBP
MDL
mg/L
MRDL
MRDLG
MRL
NPDWR
OGWDW
OPP
PQL
PE
PT
PWS
RfD
SDWA
SSCT
SYR1
SYR2
SYR3
TT
TTHM
WHO
Abbreviations and Acronyms
best available technology
disinfection byproduct
Disinfectants/Disinfection Byproducts Rule
U.S. Environmental Protection Agency
estimated quantitation level
Haloacetic Acids (five) (sum of monochloroacetic acid, dichloroacetic
acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic
acid)
health effects assessment
Hazardous Substances Data Bank
International Agency for Research on Cancer
information collection request
Integrated Risk Information System
maximum contaminant level
maximum contaminant level goal
microbial and disinfection byproduct
method detection limit
milligrams per liter
maximum residual disinfectant level
maximum residual disinfectant level goal
minimum reporting level
national primary drinking water regulation
Office of Ground Water and Drinking Water
Office of Pesticide Programs
practical quantitation level
performance evaluation
proficiency testing
public water system
reference dose
Safe Drinking Water Act
small system compliance technology
Six-Year Review 1
Six-Year Review 2
Six-Year Review 3
treatment technique
total trihalomethanes (sum of four THMs: chloroform,
bromodichloromethane, dibromochloromethane, and bromoform)
World Health Organization
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Executive Summary
The 1996 Safe Drinking Water Act (SDWA) Amendments require the U.S. Environmental
Protection Agency (EPA or the Agency) to periodically review existing national primary
drinking water regulations (NPDWRs) and determine which, if any, need to be revised. The
purpose of the review, called the Six-Year Review, is to identify those NPDWRs for which
current health effects assessments, changes in technology and/or other factors provide a health or
technical basis to support a regulatory revision that will improve or strengthen public health
protection. EPA completed and published the results of its first Six-Year Review ("Six-Year
Review 1 (SYR1)") on July 18, 2003 (USEPA, 2003a), after developing a systematic approach,
or protocol, for the review of NPDWRs. EPA incorporated minor refinements into the protocol
and completed its second review ("Six-Year Review 2 (SYR2)") in December 2009 (published
March 2010) (USEPA, 2010). As described in this document, EPA applies the same protocol
with additional clarifications to its third Six-Year Review of NPDWRs ("Six-Year Review 3
(SYR3)").
In the Six-Year Review 3, EPA addresses the following:
• Maximum Contaminant Level Goals (MCLGs; the health goal) - for some contaminants,
new health effects assessments, completed after the MCLG was promulgated or last revised,
result in revisions to the reference doses (RfD) and/or cancer classification that could justify
a revised MCLG.
• Maximum Contaminant Levels (MCLs; the enforceable standard) - for some contaminants,
the MCL is equal to the MCLG, and the health effects assessment indicates potential to
revise the MCLG. Improvements in analytical or treatment feasibility may also indicate it is
feasible to set the MCL closer to the MCLG.
• Maximum Residual Disinfectant Level Goal (MRDLG) - these goals, which are applicable
to drinking water disinfectants, were reviewed in a manner similar to that noted above for
MCLGs. For the purpose of the protocol, discussions of the review for MCLGs should be
assumed to also incorporate the review of MRDLGs.
• Maximum Residual Disinfectant Level (MRDL) - these levels, which are applicable to
drinking water disinfectants, were reviewed in a manner similar to that noted above for
MCLs. For the purpose of the protocol, discussions of the review for MCLs should be
assumed to also incorporate the review of MRDLs.
• Treatment Technique (TT; sometimes established in lieu of or in addition to an MCL) -
information on health effects, analytical feasibility or treatment feasibility may suggest a
possibility to revise a TT.
• Other Treatment Technology (NPDWRs specify best available technologies, or BATs,
capable of achieving MCLs) - Changes to BAT recommendations may be appropriate for
revised MCLs.
• Other Regulatory Requirements (e.g., monitoring) - Revisions to other regulatory
requirements may be appropriate if information suggests that changes in requirements such
as monitoring standards (e.g., frequency) could reduce health risks or costs while maintaining
or improving the level of public health protection.
ES-1
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
The EPA updated the regulatory review decision tree as part of the Six-Year Review 3. The
decision tree contains branches with a series of sequential questions that inform a decision about
the appropriateness of revising an NPDWR. The order of the questions within the tree reflects
the sequential relationships between the different NPDWR elements and thus avoids unnecessary
analyses. The decision tree contains ten branches, including a new branch for risk-balancing,
which reflects some of the efforts related to the microbial and disinfection byproduct (MDBP)
rules.
For example, EPA must generally set the MCL as close to the MCLG as feasible. Consequently,
if the MCL is equal to the MCLG, EPA must make decisions regarding the availability and
adequacy of information relevant to the potential to revise the MCLG before making decisions
regarding the potential to revise the MCL. In addition, if there is no potential to revise the
MCLG and the MCL is already equal to the MCLG, then there is no basis for revising the MCL.
In this instance, the "branch" of the decision tree containing questions about revising the MCL is
not reached, and it is not necessary to review information related to analytical feasibility.
The first branch of the decision tree is an Initial Review Branch, with the purpose of identifying
NPDWRs for which further review of detailed technical data is premature (for example, the
NPDWR is the subject of recent or ongoing rulemaking, or there is an ongoing health effects
assessment and the MCL is already set equal to the MCLG). Excluding such NPDWRs from
subsequent review prevents duplicative agency efforts.
The branches of the decision tree are:
• Initial review,
• Health effects and MCLG,
. MCL,
• Treatment technique,
• Treatment technique analysis,
• Methods,
• Occurrence,
• Treatment,
• Risk-balancing, and
• Implementation.
The Six-Year Review 3 results identify which NPDWRs, if any, are candidates for revision and
specify those NPDWRs for which no action is to be taken at this time. A recommendation to
revise a NPDWR starts a regulatory process that involves more detailed analyses concerning
health effects, costs, benefits, occurrence and other matters relevant to deciding whether and how
a NPDWR should be revised. At any point in this process, EPA may find that regulatory
revisions are not appropriate and may discontinue regulatory revision efforts. Review of that
NPDWR would, however, continue in future Six-Year Reviews.
ES-2
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Similarly, a recommendation to "take no action at this time" means only that EPA does not
believe that regulatory changes to a particular NPDWR are appropriate based on health effects,
analytical methods, treatment data, ongoing scientific reviews, priority or other reasons. The
EPA Administrator has the discretion to determine which revisions are appropriate, and may
consider a variety of factors. These factors include but are not limited to the type of health effects
on the general population and sensitive populations and life stages, including children; the
geographical distribution of the affected systems and populations; the size of the affected
populations; and competing agency priorities and resource constraints.
Reviews of these NPDWRs in future Six-Year Reviews may lead to a recommendation that
regulatory changes are appropriate.
ES-3
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
1 Introduction
The 1996 SDWA Amendments require the EPA to periodically review existing NPDWRs.
Section 1412(b)(9) of the SDWA reads:
,..[t]he Administrator shall, not less than every 6 years, review and revise, as
appropriate, each primary drinking water regulation promulgated under this title.
Any revision of a national primary drinking water regulation shall be promulgated
in accordance with this section, except that each revision shall maintain, or
provide for greater, protection of the health of persons.
Pursuant to the 1996 SDWA Amendments, EPA completed and published the results of its first
Six-Year Review on July 18, 2003 (USEPA, 2003a), after developing a systematic approach, or
protocol, for the review of NPDWRs. EPA incorporated minor refinements into the protocol and
completed its second review in December 2009 (USEPA 2010). In its third Six-Year Review of
NPDWRs, EPA uses the same protocol as was used in the SYR2, with minor clarifications.
Section 2 provides an overview of the protocol and Section 3 provides a more detailed discussion
of the decision tree implementing the protocol as used for the Six-Year Review 3. The Agency
intends to continue to refine the protocol during subsequent Six-Year Reviews to address
changing circumstances.
1.1 Basic Principles
The primary goal of the Six-Year Review process is to identify which NPDWRs, if any, are
candidates for revision. Although the statute does not define when a revision is "appropriate," as
a general benchmark, EPA considers a possible revision to be "appropriate" if, at a minimum, it
presents a meaningful opportunity to:
• improve the level of public health protection, and/or
• achieve cost savings while maintaining or improving the level of public health protection.
Toward this end, EPA applied a number of basic principles in reviewing NPDWRs. First, the
Agency sought to avoid redundant review efforts. Therefore, EPA classified NPDWRs that were
the subject of other rulemaking actions either ongoing or completed during this review period as
having "ongoing actions" or "recent actions" and not subject to further technical review under
the Six-Year Review 3.
Second, EPA evaluated the potential for new information to affect NPDWRs in a manner
consistent with its existing policies and procedures for developing NPDWRs. For example, in
determining whether a possible change in analytical feasibility existed, the Agency applied the
current policies and procedures for calculating the practical quantitation level for NPDWRs.
1-1
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Third, the Agency does not believe it is appropriate to consider revisions to NPDWRs for
contaminants with an ongoing health effect assessment and for which the MCL is set equal to the
MCLG or based on benefit-cost analysis. This principle stems from the fact that any new health
effects information could affect the MCL via a change in the MCLG or the assessment of the
benefits associated with the MCL. Therefore, EPA made a "take no action" recommendation if
the health effect assessment would not be completed during the review period for each
contaminant that has either an MCL that is equal to its MCLG or an MCL that is based on the
provisions in the 1996 SDWA Amendments (SDWA §1412(b)(6)(A)).
Fourth, EPA will address new information from health effect assessments completed after the
information cutoff date (December 2015) for the Six-Year Review 3 and any new conclusions or
additional information associated with the NPDWR during the next review cycle.
Fifth, EPA identified areas of inadequate or unavailable data (data gaps) or emerging data that
are needed to determine whether revision to an NPDWR is appropriate. If EPA is able to fill such
gaps or fully evaluate the emerging information after completing the Six-Year Review 3, the
Agency will consider the information as part of the next review cycle.
EPA may consider accelerating a review and possible revision for a particular NPDWR before
the next review cycle if a review and possible revision is justified by new public health risk
information.
Finally, EPA applied the Agency's peer review policy (USEPA, 2015), where appropriate, to any
new analyses.
1.2 Scope of Review
Consistent with the Six-Year Review 1 and the Six-Year Review 2, the Six-Year Review 3
encompasses the individual elements of NPDWRs, as follows:
• MCLG changes - EPA generally considers changes to the MCLG (the health goal) only in
instances when a new health effects assessment, completed after the MCLG was promulgated
or last revised, results in a revised RfD and/or cancer classification.
• MCL changes - EPA generally considers changes to the MCL (the enforceable standard)
whenever: (1) the health effects assessment justifies a possible change to the MCLG and the
existing MCL is set at the MCLG or (2) the current MCL was limited by analytical or
treatment feasibility and the review of these capabilities indicates that it may now be feasible
to set the MCL closer to the MCLG.1
• Maximum Residual Disinfectant Level Goal - EPA generally considers changes to the
MRDLG (the health goal for disinfectants) in a manner similar to that noted above for
MCLGs. For the purpose of the protocol, discussions of the review for MCLGs should be
assumed to also incorporate the review of MRDLGs.
1 Although the 1996 SDWA Amendments allow EPA in certain circumstances to set the MCL at a level higher than
the feasible level if the benefits do not justify the costs, the SDWA precludes the Agency from lessening the public
health protection of an existing standard (SDWA § 1412(b)(9)).
1-2
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
• Maximum Residual Disinfectant Level - EPA generally considers changes to the MRDL
(the enforceable standard for disinfectants) in a manner similar to that noted above for
MCLs. For the purpose of the protocol, discussions of the review for MCLs should be
assumed to also incorporate the review of MRDLs.
• Treatment Technique2 changes - Treatment techniques can improve to the point where
more protective drinking water standards may be considered. EPA generally considers
revisions to TT requirements whenever there is new information on health effects, analytical
feasibility or treatment feasibility that suggests a possibility to revise the TT.
• Changes to Other Treatment Technology - When EPA sets an MCL, the NPDWR also
contains BAT recommendations that address drinking water treatment processes. Although
not required for compliance purposes, EPA sets BATs that have the capability to meet
MCLs. EPA generally limits review of BAT recommendations to those NPDWRs with
possible MCL revisions.
• Changes to Other Regulatory Requirements - EPA generally considers changes to other
regulatory requirements, such as changes to monitoring requirements, if other possible
NPDWR revisions or health effects information suggest that such changes (e.g., increased
frequency in monitoring) could reduce health risks or costs while maintaining or improving
the level of public health protection. This part of the review focuses on implementation-
related issues that are not being addressed, or have not been addressed, through alternative
mechanisms (e.g., as part of a recent or ongoing rulemaking). Where appropriate alternative
mechanisms do not exist, EPA generally considered implementation-related concerns if the
possible revision meets the following criteria:
• The possible revision indicates a change to an NPDWR, as defined under section 1401 of
the SDWA;
• The possible revision was "ready" for rulemaking - that is, the problem to be resolved has
been clearly identified and specific option(s) formulated to address the problem; and
• The possible revision could improve the level of public health protection or represents a
cost savings, while maintaining or improving public health protection.
For the Six-Year Review 3, EPA reviewed the 88 chemical, microbiological and radiological
NPDWRs shown in Exhibit 1.1.
Exhibit 1.1 NPDWRs Included in the Six-Year Review 3
Contaminants/
MCLG
MCL or
TT
(mg/L)23
Contaminants/
MCLG
MCL or
TT
(mg/L)23
Parameters
(mg/L)13
Parameters
(mg/L)3
Acrylamide
0
TT
Ethylbenzene
0.7
0.7
Alachlor
0
0.002
Ethylene dibromide (EDB)
0
0.00005
Alpha/photon emitters
0 (pCi/L)
15 (pCi/L)
Fluoride
4.0
4.0
Antimony
0.006
0.006
Giardia lamblia4
0
TT
Arsenic
0
0.01
Glyphosate
0.7
0.7
2 A TT specifies a type of treatment (e.g., filtration, disinfection or other methods of control to limit contamination
in drinking water) and means for ensuring adequate treatment performance (e.g., monitoring of water quality to
ensure treatment performance).
1-3
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Contaminants/
Parameters
MCLG
(mg/L)13
MCL or
TT
(mg/L)23
Contaminants/
Parameters
MCLG
(mg/L)3
MCL or
TT
(mg/L)23
Asbestos
7 (million
fibers/L)
7 (million
fibers/L)
Haloacetic acids (HAA5)
n/a5
0.06
Atrazine
0.003
0.003
Heptachlor
0
0.0004
Barium
2
2
Heptachlor epoxide
0
0.0002
Benzene
0
0.005
Heterotrophic bacteria6
n/a
TT
Benzo[a]pyrene
0
0.0002
Hexachlorobenzene
0
0.001
Beryllium
0.004
0.004
Hexachlorocyclopentadiene
0.05
0.05
Beta/photon emitters
0 (millirems
/yr)
4 (millirems
/yr)
Lead
0
TT
Bromate
0
0.01
Legionella
0
TT
Cadmium
0.005
0.005
Lindane
0.0002
0.0002
Carbofuran
0.04
0.04
Mercury (inorganic)
0.002
0.002
Carbon tetrachloride
0
0.005
Methoxychlor
0.04
0.04
Chloramines
4
4
Monochlorobenzene
(Chlorobenzene)
0.1
0.1
Chlordane
0
0.002
Nitrate (as N)
10
10
Chlorine
4
4
Nitrite (as N)
1
1
Chlorine dioxide
0.8
0.8
Oxamyl (Vydate)
0.2
0.2
Chlorite
0.8
1
Pentachlorophenol
0
0.001
Chromium (total)
0.1
0.1
Picloram
0.5
0.5
Copper
1.3
TT
Polychlorinated biphenyls
(PCBs)
0
0.0005
Cryptosporidium
0
TT
Radium
0 (pCi/L)
5 (pCi/L)
Cyanide
0.2
0.2
Selenium
0.05
0.05
2,4-
Dichlorophenoxyacetic
acid (2,4-D)
0.07
0.07
Simazine
0.004
0.004
Dalapon
0.2
0.2
Styrene
0.1
0.1
Di(2-ethylhexyl)adipate
(DEHA)
0.4
0.4
2,3,7,8-TCDD (Dioxin)
0
3.00E-08
Di(2-
ethylhexyl)phthalate
(DEHP)
0
0.006
T etrachloroethylene
0
0.005
l,2-Dibromo-3-
chloropropane (DBCP)
0
0.0002
Thallium
0.0005
0.002
1,2-Dichlorobenzene (o-
Dichlorobenzene)
0.6
0.6
Toluene
1
1
1,4-Dichlorobenzene (p-
Dichlorobenzene)
0.075
0.075
Total coliforms (under
ADWR7 and RTCR8)
n/a
TT
1,2-Dichloroethane
(Ethylene dichloride)
0
0.005
Total Trihalomethanes
(TTHM)
n/a9
0.08
1,1 -Dichloroethylene
0.007
0.007
Toxaphene
0
0.003
cis-1,2- Dichloroethylene
0.07
0.07
2,4,5-TP (Silvex)
0.05
0.05
trans-1,2-
Dichloroethylene
0.1
0.1
1,2,4-Trichlorobenzene
0.07
0.07
1-4
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Contaminants/
Parameters
MCLG
(mg/L)13
MCL or
TT
(mg/L)23
Contaminants/
Parameters
MCLG
(mg/L)3
MCL or
TT
(mg/L)23
Dichloromethane
(Methylene chloride)
0
0.005
1,1,1 -T richloroethane
0.2
0.2
1,2-Dichloropropane
0
0.005
1,1,2-Trichloroethane
0.003
0.005
Dinoseb
0.007
0.007
T richloroethylene
0
0.005
Diquat
0.02
0.02
Turbidity
n/a
TT
E. coli
MCL10 and
TT8
Uranium
0.030
Endothall
0.1
0.1
Vinyl Chloride
0.002
Endrin
0.002
0.002
Viruses
0
TT
Epichlorohydrin
0
TT
Xylenes (total)
10
10
1.
MCLG: the maximum level of a contaminant in drinking water at which no known or anticipated adverse
effect on the health of persons would occur, allowing an adequate margin of safety.
MCL: the maximum level allowed of a contaminant in water which is delivered to any user of a public water
system.
TT: an enforceable procedure or level of technological performance which public water systems must follow
to ensure control of a contaminant.
Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts
per million. For chlorine, chloramines and chlorine dioxide, values presented are MRDLG and MRDL.
The current preferred taxonomic name is Giardia duodenalis, with Giardia lamblia and Giardia intestinalis
as synonymous names. However, Giardia lamblia was the name used to establish the MCLG in 1989.
Elsewhere in this document, this pathogen will be referred to as Giardia spp. or simply Giardia unless
discussing information on an individual species.
There is no MCLG for all five haloacetic acids. MCLGs for some of the individual contaminants are:
dichloroacetic acid (zero), trichloroacetic acid (0.02 mg/L) and monochloroacetic acid (0.07 mg/L).
Bromoacetic acid and dibromoacetic acid are regulated with this group, but have no MCLGs.
Includes indicators that are used in lieu of direct measurements (e.g., of heterotrophic bacteria, turbidity).
The Aircraft Drinking Water Rule (ADWR) 40 CFR Part 141 Subpart X, promulgated October 19, 2009,
covers total coliforms.
Under the RTCR, a PWS is required to conduct an assessment if it exceeded any of the TT triggers identified
in 40 CFR § 141.859(a). It is also required to correct any sanitary defects found through the assessment.
There is no MCLG for total trihalomethanes (TTHM). MCLGs for some of the individual contaminants are:
bromodichloromethane (zero), bromoform (zero), dibromochloromethane (0.06 mg/L) and chloroform (0.07
mg/L).
10. A PWS is in compliance with the E. coli MCL unless any of the conditions identified under 40 CFR
§141.63(c) occur.
2.
3.
4.
5.
9.
1-5
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
1.3 Organization and Contents of this Document
This document describes the review process for the Six-Year Review 3:
• Section 2 provides an overview of the Six-Year Review protocol and the decision tree EPA
developed to implement it for the Six-Year Review 3; and
• Section 3 provides detailed description of the individual branches of the decision tree
implementing the Six-Year Review 3 protocol.
This document does not summarize the review results from each branch of the Six-Year Review
3; please see support documents for results (USEPA, 20163).
3 EPA developed multiple support documents to support the SYR3—see references USEPA, 2016a to USEPA,
2016rinthe reference section.
1-6
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
2 Overview of the Six-Year Review Protocol
During the Six-Year Review 1, the Agency developed a systematic approach or protocol to
review existing NPDWRs (USEPA, 2003b). The Agency based this protocol on the
recommendations of the National Drinking Water Advisory Council, through internal agency
deliberations, and discussions with a diverse group of stakeholders involved in drinking water
and its protection.
For the Six-Year Review 2, EPA assessed the protocol and determined that it remained
appropriate and suitable for the second review. Thus, the information requirements and decision-
making process of the Six-Year Review 2 protocol were essentially the same as those
implemented during the Six-Year Review 1, with some minor refinements to enhance the
Agency's effectiveness in applying the protocol to the review of NPDWRs (USEPA, 2009).
For the Six-Year Review 3, EPA again assessed the protocol and determined that it remained
generally appropriate and suitable for the third review. Thus, the decision-making processes of
the Six-Year Review 3 protocol were essentially the same as those implemented during the Six-
Year Review 1 and the Six-Year Review 2, with some clarifications to the elements related to the
review of NPDWRs for the MDBP rules.
The Six-Year Review 3 protocol addresses critical aspects of health protection and the setting of
standards under the SDWA. The results of the Six-Year Review 3 identify NPDWRs that are
candidates for revision and those for which no action is recommended at this time.
The publication of candidates for revision pursuant to a Six-Year Review under Section
1412(b)(9) is not the end of the regulatory process, but rather the beginning; it starts a regulatory
process that involves more detailed analyses concerning health effects, costs, benefits,
occurrence, and other matters relevant to deciding whether and how an NPDWR should be
revised. At any point in this process, EPA may find that regulatory revisions are not appropriate
and may discontinue regulatory revision efforts. Review of that NPDWR would, however,
resume in future Six-Year Reviews.
Similarly, a recommendation to "take no action at this time" means that EPA does not believe
that regulatory changes to a particular NPDWR are appropriate at this time due to a lack of new
health effects, analytical methods or treatment data; lack of contaminant occurrence at levels of
concern; ongoing scientific reviews; limited opportunity to reduce health risks; limited
opportunity to reduce costs while maintaining the same or greater level of health protection; low
priority; or other reasons. Reviews of these contaminants in future Six-Year Reviews may lead to
a recommendation that regulatory changes are appropriate.
The Agency will continue to refine the Six-Year Review protocol during subsequent reviews to
address changing circumstances.
2-1
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
2.1 Protocol Clarifications for the Six-Year Review 3
During the Six-Year Review 2, EPA refined the protocol to implement a more detailed "decision
tree" than it used during the Six-Year Review 1. The revised protocol was broken down into a
series of questions that informs a decision about the appropriateness of revising an NPDWR.
These questions were logically ordered into a decision tree that incorporated the sequential
relationships between the different NPDWR elements.
During the Six-Year Review 3, EPA clarified the protocol to address concepts specific to the
MDBP rules. While retaining the same branches as were used in the Six-Year Review 2,
clarifications were made to the protocol to address situations such as: where there are MCLGs
for individual contaminants in a group (that might warrant a change) but only an MCL for the
group (such as with TTHM or HAA5); where there is a potential for a treatment technique
revision (in addition to, or instead of, an MCL revision); and where the health risk is identified in
terms of the strength of the weight of evidence. In addition, the protocol was clarified to consider
the use of indicators for groups of disinfection byproducts (DBPs), including regulated and
unregulated DBPs and to consider risk-balancing between MDBP requirements, or among
differing types of DBPs.
2.2 Elements of the Six-Year Review 3 Decision Tree
The Six-Year Review decision tree contains "branches" with multiple questions for each review
topic. Information flows between these branches and results in the NPDWR identified as either a
candidate for revision or not a candidate for revision ("no action at this time"). Exhibit 2.1 shows
the flow of information between branches where the result is a NPDWR as a candidate for
revision. More details about the flow of information within each individual branch are found in
exhibits within each section of the document. Each branch corresponds to a specific technical
review of an NPDWR element that EPA conducted during the Six-Year Review 3. The following
branches comprise the decision tree:
• Initial review,
• Health effects and MCLG,
. MCL,
• Treatment technique,
• Treatment technique analysis,
• Methods,
• Occurrence,
• Treatment,
• Risk-balancing, and
• Implementation.
2-2
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
One of the key factors determining how an existing NPDWR moves through the Six-Year
Review decision tree is whether an NPDWR involves an MCL or a TT requirement, since some
of the branches are applicable to only one of those two types of requirements. For example, those
NPDWRs that only involve an MCL will complete all branches mentioned in the list above
including the MCL-related branches of MCL, Methods, Occurrence and Treatment but excluding
the TT-related branches of Treatment Technique and Treatment Technique Analysis.
Conversely, the NPDWRs that only involve a TT (e.g., NPDWRs related to microbial regulation)
will complete all branches mentioned in the list above including the TT-related branches of
Treatment Technique and Treatment Technique Analysis but excluding the MCL-related
branches of Methods, Occurrence and Treatment. NPDWRs that only involve a TT will also not
complete a large majority of the MCL Branch.
Another factor determining how an existing NPDWR moves through the Six-Year Review
decision tree is whether an NPDWR is an MDBP. If an NPDWR is an MDBP it will complete
the Risk-balancing Branch in its entirety. If an NPDWR is not an MDBP, a majority of the Risk-
balancing Branch will not be completed, as this branch is applicable only to the review of the
MDBP NPDWRs.
The following sections describe each branch and provide detailed descriptions of EPA's data
requirements, analyses and decision-making process.
2-3
-------
EPA-OGWDW
EPA Protocol for the Third Review of Existing
National Primary Drinking Water Regulations
EPA 810-R-16-007
December 2016
Exhibit 2.1 Process for Identifying NPDWRs that are Candidates for Revision
/ Occurrence Branch \
Identifies whether MCL
revisions present a
meaningful opportunity to
reduce health risks or costs
, based on occurrence ,
\ estimates. /.
/ Methods Branch \
identifies potential to revise
practical quantitation level
based on new monitoring
data or previous data
\ analysis. /
Treatment Branch
Identifies potential treatment
technologies to meet
alternative MCLs.
NPDWR
candidate for
revision
Starting point for
all NPDWRs*
Initial Review Branch
Identifies NPDWRs
undergoing EPA action or
assessment that should be
excluded from review and
those that should be
reviewed further.
Health Effects and
MCLG Branch
Identifies NPDWRs with
potential for MCLG revision
(MCL Branch 1) and those
without (MCL Branch 2).
Risk-Balancing Branch
For MDBP NPDWRs only,
identifies potenial risk-
balancing considerations
among MDBPs (regulated
and unregulated!.
Implementation Branch
Identifies potential impacts
on monitoring/reporting
requirements, requiring
further MCL and/or TT
revisions to be considered.
MCL Branch 1 or 2
Identifies NPDWRs with
potential for MCL revision
and those without. NPDWRs
with IT are directed to the
Treatment Technique
Branch.
At any point, an outcome of 'no action at this time' can be made
based on individual branch exclusion criteria, meaning the
NPDWR is not a candidate for revision for this review cycle.
T reatment T echniqua
Branch
Identifies NPDWRs with
potential forTT revision and
those without.
Treatment Technique
Analysis Branch
Identifies whether TT
revisions present a
meaningful opportunity to
reduce health risks or costs .
based on treatment
technologies.
2-4
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
3 Detailed Discussion of Decision Tree Implementing the
Protocol
This section describes the individual branches of the decision tree in detail, including the
purpose, inputs and outputs of each branch.
3.1 Initial Review Branch
The purpose of the Initial Review Branch (Exhibit 3.1), is to identify NPDWRs that meet one of
three conditions for which further review is premature. The three conditions are:
• The NPDWR was recently completed, reviewed or revised (i.e., since August 2008);
• The NPDWR is part of an ongoing or pending regulatory action; or
• The NPDWR contaminants has an ongoing EPA health effects assessments that is due after
the cutoff date for the review or EPA completed a health effects assessment but then
identified new information with the potential to affect the MCLG and the MCL is set equal to
the MCLG.
Excluding such NPDWRs from the review process prevents duplicative agency efforts associated
with these three conditions.
3.1.1 Inputs to the Initial Review
The questions in the Initial Review Branch are screening-level questions that EPA answered for
each NPDWR. The beginning questions in the branch require information regarding whether an
NPDWR is the subject of recent, ongoing or pending regulatory actions.
3-1
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.1 Initial Review Branch
Was a regulatory action
undertaken since
August 2008?
/Recent/S
ongoing or
pending
regulatory
Vaction/
Is a regulatory reviewer
revision in progress or
planned through 2015?
GO TO MCL Branch 2
Is a newHEA [including
reproductive and developmental
effects] in progress and
expected sifter December 2015.
or is there new information*
after completion of a new HEA?
Continue
review
Is MCLG
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Health effects assessments are conducted outside the scope of the Six-Year Review process and
follow EPA guidelines established to assess risks for different health effects, different exposure
routes, and in different sensitive population groups and life stages including children. To inform
the Six-Year Review process, EPA tracks the status of these health effect assessments and
provides summaries that identify the contaminants with ongoing health effect assessments and
their expected completion dates.
3.1.2 Output of Initial Review
The outputs of the initial review branch are: (1) a list of NPDWRs excluded from further review
branches during the current cycle,4 (2) a list of NPDWRs that proceed to the Health Effects and
MCLG branch for questions about the potential to revise the MCLG and (3) a list of NPDWRs
that proceed to the MCL Branch 2 (No MCLG Revision) despite ongoing health effects
assessments because they have MCLs that are greater than their respective MCLGs.
3.2 Health Effects and MCLG Branch
The primary purpose of the Health Effects and MCLG Branch (Exhibit 3.2) is to identify the
NPDWRs for which there is potential to revise the MCLG. To do this, the protocol requires that:
• A revised or new health effects assessment be completed during the current cycle, after
August 2008 and before December 2015, and
• The assessment results in a change to the RfD or cancer risk.
The protocol provides an option to revisit agency decisions to take no action for contaminants
that had a new health effects assessment that indicated potential for an MCLG revision during
the prior cycle.
The Health Effects and MCLG Branch also identifies whether there is new health effects
information identified during a review of peer-reviewed literature that leads to a nomination for a
new health effects assessment for those contaminants for which there are no recent or ongoing
assessments. This would also address situations where there is new health-related information
associated with the data on which the MCL or TT was based, such as the weight of evidence
information used to support the development of MDBP rules.
4 NPDWRs that have a "Take no action at this time" result on the Initial Review may still be affected by a cross-
cutting issue affecting multiple NPDWRs that qualifies for consideration under the conditions described for other
regulatory revisions.
3-3
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.2 Health Effects and MCLG Branch
Consider
MCLG
revision
Take no
action on
MCLG
GO TO MCL Branch 1
GO TO MCL Branch 2
Nominate for IRIS/0PP/0W review
HEA since SYR2 cutoff of
August 2008?
Any change in the current
HEA (i.e., RfD change or
nonlinear mode of action) that
suggests MCLG change?
Perform full toxicological
search or update SYR2
information. New
information*?
Did a previous round suggest
MCLG revision but reject it
because of constraints on the
MCL?
Is there new information*
indicating a nonlinearmode of
action or potential
reproductive/developmental
effects?
Key:
Yes
'New information that could affect the MCLG. May need to re-nominate for IRIS/OPP/OW review
based on this new information.
3.2.1 Inputs to Health Effects and MCLG Review
The first question in the Health Effects and MCLG Branch identifies the NPDWRs having a
formal health effects and toxicological assessment completed during the current review cycle.
For regulated contaminants that have a new health effects assessment, this branch asks whether
there was a change in toxicological parameters that affect the MCLG, including conditions such
as:
• Whether the assessment resulted in changes to the RfD or cancer classification, and
• Whether these changes would potentially affect the MCLG.
EPA obtained RfD and cancer classification information from its own formal health effects
assessments such as IRIS and OPP. EPA also evaluated relevant non-EPA assessments such as
the Agency for Toxic Substances and Disease Registry, California Environmental Protection
Agency, Health Canada, World Health Organization (WHO), National Toxicology Program and
International Agency for Research on Cancer.
If there were no new cancer data or studies for the SYR3 evaluation, EPA retained the cancer
classification of the NPDWR based on 1986 cancer risk classifications (USEPA, 1986):
Category I (Human carcinogen or Probable human carcinogen), Category II (Possible human
carcinogen) and Category III (Not classifiable as to human carcinogenicity or evidence of non-
carcinogenicity for humans). In some instances, a combination of the 1986 classification and the
3-4
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
draft 1999 classification (USEPA, 1999) was used (e.g., for the MDBP rules, depending on
whether the regulation was part of the Stage 1 and Stage 2 Disinfectants and Disinfection
Byproducts Rules (D/DBPR)). If there were new cancer data or studies, EPA could recommend a
cancer risk evaluation following the 2005 cancer guidelines and the supplemental guidelines,
where appropriate (USEPA, 2005).
Another question in this branch divides NPDWRs that did not have a recent health effects
assessment into two categories:
• Those with nonzero MCLGs, including non-carcinogens or carcinogens with threshold, and
• Those with MCLGs of zero, e.g., linear low-dose carcinogens.
Subsequent questions address whether literature searches indicate a need for a new formal health
effects assessment. For the Six-Year Review 3, EPA conducted a review of the peer-reviewed
literature on relevant health effects (i.e., general toxicity, reproductive and developmental
toxicity, and cancer risk via an oral route for the general population and sensitive subpopulation
groups including children). This review searched for new health effects information indicating
that the current RfD values or cancer risk categories might not adequately represent health risks.
EPA's review for each chemical began with reviews or assessments using the following sources:
IRIS, OPP, the Office of Radiation and Indoor Air, National Academy of Sciences, Agency for
Toxic Substances and Disease, National Toxicology Program, National Institute of
Environmental Health Sciences, California Environmental Protection Agency, WHO, European
Commission Concise International Chemical Assessment Documents, International Programme
on Chemical Safety/Environmental Health Criteria, International Agency for Research on
Cancer, Health Canada, Joint Expert Committee on Food Additives, and Joint Food and
Agriculture Organization of the United States/WHO Meeting on Pesticide Residues. EPA
obtained each organization's most recent assessment available. EPA also conducted literature
searches to identify primary literature to supplement the information in the authoritative reviews.
The searches utilized the following databases: TOXLINE, MEDLINE®, Developmental and
Reproductive Toxicology, Chemical Carcinogenesis Research Information System and
Hazardous Substances Data Bank.
The review identified two categories of contaminants, those with:
• New health effects information indicating a nonlinear mode of action or potential
reproductive/developmental or other toxicological effects for contaminants at concentrations
at or below the MCL when the MCLG is zero, and
• New cancer data or toxicological information in the literature that potentially affects the
RfDs for contaminants without a recent health effects assessment and a nonzero MCLG.
Another question in this branch identifies contaminants for which there was not a new health
effects assessment in the current review cycle, but there was one during the previous review
cycle that included a change in the RfD. During the Six-Year Review 2, EPA took no action to
revise the NPDWR for some of these contaminants for one of the following reasons:
3-5
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
• The possible revision would not have provided a meaningful opportunity to reduce health
risks;
• The possible revision would not have provided a meaningful opportunity to reduce costs
while maintaining the same or greater level of health protection; or
• The possible revision would have been a low priority because of competing workload
priorities, the administrative costs associated with rulemaking, and the burden on states and
the regulated community to implement any regulatory change that resulted.
For MDBP NPDWRs, EPA examined new health-related information about epidemiological and
toxicological effects (in a manner similar to the review completed during the development of the
D/DBPRs). As discussed in the preamble to the final rule for the Stage 2 D/DBPR, EPA
promulgated the rule to provide for increased protection against the potential risks of cancer and
reproductive and developmental health effects associated with DBPs. The rule was designed to
reduce the level of exposure to DBPs without undermining the control of microbial pathogens. It
was based, in part, on the weight of evidence from epidemiological and toxicological studies
linking bladder, colon and rectal cancers to DBP exposure, as well as epidemiological and
toxicological studies showing possible associations between chlorinated drinking water and
adverse reproductive and developmental endpoints. During the Six-Year Review 3, EPA
evaluated the weight of evidence from health-related information related to those effects, for
both cancer and reproductive and developmental endpoints. EPA also examined toxicological
data for individual contaminants such as specific DBPs that are included in a group MCL
(TTHM or HAA5).
3.2.2 Outputs from Health Effects and MCLG Review
Outputs from the Health Effects and MCLG Branch consist of the following lists of NPDWRs:
• NPDWRs for which there is potential to revise the MCLG based on the availability of new
Agency health effects information or recent non-EPA assessments that include new scientific
information consistent with EPA guidelines and policies, or contaminants for which there
was a potential to revise the MCLG during a previous Six-Year Review, but for which EPA
took no action;
• NPDWRs for which a literature review indicates a potential change in health effects
information and that should, therefore, be nominated for a formal health effects assessment
through the Office of Water, IRIS or OPP; and
• NPDWRs for which there is no potential to revise the MCLG during the Six-Year Review 3.
The decision tree directs the first category of contaminants to the MCL branch that reflects
potential for MCLG revision (MCL Branch 1 - Potential for MCLG Revision). It directs the
second and third categories of contaminants to a second MCL branch that reflects no action will
be taken regarding MCLG revision (MCL Branch 2 - No Potential for MCLG Revision).
3-6
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
3.3 Maximum Contaminant Level Branches
The purpose of each MCL branch is to identify NPDWRs for which new information indicates
potential to revise the MCL. The SDWA requires that EPA generally set the MCL as close to the
MCLG as feasible [Section 1412(b)(4)(B)], Feasibility refers to both the ability to treat water to
meet the MCL and the ability to monitor water quality at the MCL. For most contaminants for
which the MCLG is greater than zero, the MCL equals the MCLG, which indicates that neither
analytical method quantitation nor treatment capabilities limit the ability to achieve the MCLG.
Conversely, when the MCLG equals zero, the MCL is usually set equal to the practical
quantitation limit (PQL), which is based on the detection capability that most laboratories can
reliably and consistently achieve using approved analytical methods within specified limits of
precision and accuracy. Thus, the PQL is the most common limiting factor with respect to
feasibility. Consequently, the MCL branches address analytical feasibility before treatment
feasibility. Additional considerations were included in development of MCLs for the D/DBPRs,
these details are described in later sections of the protocol.
The decision tree includes two MCL Branches: one for contaminants with a possible MCLG
revision (MCL Branch 1; Exhibit 3.3a), and the other for contaminants with no action regarding
the MCLG (MCL Branch 2; Exhibit 3.3b).
3-7
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.3a Maximum Contaminant Level Branch 1 (Potential for MCLG Revision)
Take no
action on
MCLf
Consider
MCL revision
Is MCL=MCLG?
Is higher MCLG indicated?
Is MCL based on
PQL?
Is standard an
MCL?
GO TO Treatment
Technique Branch
GO TO Risk
Balancing
Branch
Is there new benefits or
cost information?
Is MCL based on
treatment feasibility?
Issue a health advisory
if needed
Is MCL based on benefit-
cost analysis?
Does new information
indicate lower MCL is
feasible?
GO TO Methods Branch
and Return here. Is
PQL
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.3b Maximum Contaminant Level Branch 2 (No Potential for MCLG
Revision)
Take no
action on
MCLf
Consider
MCL revision
Is MCL based on
PQL?
Is standard an
MCL?
GO TO Treatment
Technique Branch
GO TO Risk
Balancing
Branch
Is there new benefits or
cost information?
Is MCL based on
treatment feasibility?
Is MCL based on benefit-
cost analysis?
Does new information
indicate lower MCL is
feasible?
GO TO Methods Branch
and Return here. Is
PQL
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
The MDBP rules consist of both MCL and TT standards, including situations where there are
multiple MCLGs for a given NPDWR. For TTHM, the four individual components each have
their own MCLGs, with two that are zero and two non-zero. For HAA5, there are MCLGs for
three of the five components; one is zero and the other two are non-zero. For the Six-Year
Review 3, EPA examined these MCLGs on an individual component basis, and completed an
overall health effects review. As discussed earlier for these rules, it should be noted that the
treatment techniques were reviewed in addition to the MCLs.
Subsequent questions on the MCL branches involve subordinate branches for analytical methods,
occurrence and treatment analysis that explore the availability of new information that could
affect EPA's recommendation regarding an MCL revision. Later sections of this document
address the specific data requirements of these subordinate branches and describe the analyses
that EPA conducted as part of these branches. The MCL branches combine the findings from
these subordinate branches into an overall MCL recommendation.
3.3.2 Outputs from Maximum Contaminant Level Review
The MCL branches identify contaminants for which the review did not identify any new
information indicating potential for MCL revision and those for which new information indicates
EPA should consider revising the MCL or adding complementary MCLs. After completing an
MCL branch, the decision tree directs the review to the risk-balancing branch.
3.4 Treatment Technique Branch
When a contaminant has a TT standard instead of, or in addition to, an MCL, the protocol uses
the Treatment Technique Branch of the decision tree (Exhibit 3.4), in addition to the MCL
Branches. The purpose of the Treatment Technique Branch is to identify whether there is
potential to revise a TT standard.
3-10
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.4 Treatment Technique Branch
Does new health risk,
analytical methods, or
treatment information
by December 2015
indicate possible TT
revision?
GO TO TT Analysis
Branch. Does the new
information indicate
that a meaningful
opportunity exists for
health risk or cost
reduction?
Take no
** action on TT
ConsiderTT
revision
GO TO Risk
Balancing
Branch
Yes
3-11
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
3.4.1 Inputs to Treatment Technique Review
The TT Branch includes the following questions:
• Does new information in the following areas indicate potential for TT revision: health risk,
analytical methods or treatment technique?
• Based on the decisions on the Treatment Technique Analysis Branch, does a meaningful
opportunity exist for health risk or cost reduction?
The following NPDWRs have a TT in lieu of an MCL: acrylamide, copper, Cryptosporidium,
epichlorohydrin, Giardia lamblia, lead, Legionella and viruses. In addition, the D/DBPRs
include a TT for precursors in addition to the MCLs for contaminants.
3.4.2 Outputs from Treatment Technique Review
The Treatment Technique Branch identifies NPDWRs for which EPA should consider revisions
to a TT standard because all of the following apply:
• New health, methods and/or treatment information are available that suggests revision; and
• There is a meaningful opportunity to lower health risks or costs.
The decision tree then directs the review to the Risk-Balancing Branch.
3.5 Treatment Technique Analysis Branch
The purpose of the Treatment Technique Analysis Branch (Exhibit 3.5) is to determine whether
the new information that could affect the TT standard has the potential to present a meaningful
opportunity to revise the TT standard.
3.5.1 Inputs to Treatment Technique Analysis Review
The Treatment Technique Analysis Branch includes the following questions:
• Is there a significant increase in health risk estimated from exposure to the contaminant, or
weight of evidence for health-related information on which the NPDWR was based?
• Is there a significant improvement in analytical or treatment feasibility?
The first question identifies whether new health effects information indicates health risks that are
significantly different from those considered at the time EPA promulgated the NPDWR. The
second question addresses whether there are significant changes in analytical feasibility
constraints that might have originally led to a contaminant having a TT standard in lieu of an
MCL. It also addresses whether significant changes in treatment feasibility indicate potential for
revision to the TT standard.
3-12
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.5 Treatment Technique Analysis Branch
Meaningful
opportunity
exists for TT
„ revision >
meaningful
opportunity
exists for TT
\ revision /
Return to TT
Branch
Key:
-~ Yes
Is there a significant
improvements
analytical feasibility
or treatment
techniques?
Is there a significant
increase in health risk
estimated from
exposure to the
contaminant?
3.5.2 Outputs from Treatment Technique Analysis Review
The Treatment Technique Analysis Branch identifies contaminants for which new information
may present a meaningful opportunity to lower health risks or costs through a TT revision. The
decision tree then directs the review back to the main Treatment Technique Branch.
3.6 Methods Branch
The purpose of the Methods Branch (Exhibit 3.6) is to determine whether there is potential to
revise the PQL for a regulated contaminant. The PQL is the level at which laboratories can
reliably and consistently measure a chemical contaminant in drinking water. This is usually
interpreted as the analyte concentration at which 75 percent of laboratories can measure
concentration within the promulgated acceptance criteria.
3-13
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.6 Methods Branch
There is
potential to
revise PQL
Cannot revise
PQL
Return to source
(MCL1 orMCL 2)
Are new monitoring
data available by
December 2015?
Did analysis prior
round indicate potential
to revise PQL?
Key:
Yes
Do MDL and/or MRL
data suggest
quantitation levels
belowthePQL?
Do PT data available by
December 2015 support
quantitation levels below
the PQL?
The branch considers two categories of contaminants:
• Contaminants for which the MCL is limited by analytical feasibility (e.g., the MCL is set at
the PQL), and the MCLG is still appropriate, and
• Contaminants for which the health effects review indicated potential to change the MCLG
and the current PQL is above possible MCLG values.
EPA reviews and approves analytical methods under a separate regulatory process. Therefore,
the Six-Year Review 3 did not include a review to determine whether the approved analytical
methods themselves can be revised. Historically, EPA has used two main approaches to
determine a PQL for the SDWA analytes: (1) Performance Evaluation (PE) data from Water
Supply studies is the preferred alternative when sufficient data are available; or (2) a multiplier
method, in which the PQL is calculated by multiplying the EPA-derived method detection limit
(MDL) by a factor of 5 or 10 (USEPA, 1985; USEPA, 1987; USEPA, 1989). Using PE data to
derive the PQL for chemical NPDWRs involves determining the concentration of an analyte at
which 75 percent of EPA Regional and state laboratories achieve results within a specified
acceptance window (USEPA, 1989).
3-14
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
3.6.1 Inputs to Methods Review
The Methods Branch includes the following questions:
• Are new monitoring data available by the cutoff date (December 2015) that EPA selected for
the Six-Year Review 3?
• Do the new analytical methods data indicate potential to revise the PQL?
• Do other new data such as MDL and/or minimum reporting level (MRL) information
indicate potential to revise the PQL?
• Do previous data or analyses (i.e., the Six-Year Review 1, the Six-Year Review 2) indicate
potential to revise the PQL?
The protocol developed for the Six-Year Review 1 primarily used PE data from Water Supply
studies. These were laboratory accreditation studies conducted under EPA oversight until 1999,
when the program was privatized. The National Environmental Laboratory Accreditation
Conference currently conducts the accreditation program via Proficiency Testing (PT) studies.
For the Six-Year Review 2, EPA could not obtain actual PT study analytical results from the
National Environmental Laboratory Accreditation Conference or any PT providers. Given that
PE data and comparable PT data were not available for the Six-Year Review 2, EPA modified
the review process, as described below.
The PQL reassessments for the Six-Year Review 3 use a variety of data. The primary data
sources were:
• Laboratory passing rates based on PT data (i.e., the percent of laboratories passing a
proficiency test for a given study) from 2008 through 2014, and
• Analytical method feasibility data (i.e., MRLs and MDLs) collected as part of the Six-Year
Review information collection request (ICR).
EPA first reviewed the PT passing rate results for tests conducted at and below the current PQL
to indicate potential for PQL revision. EPA placed contaminants into one of three categories
based on whether the PT and PE data supported, may support, or did not support a lower PQL.
For example, EPA placed contaminants with passing rates above 75 percent for PT studies with
true values below the PQL in the "PQL reassessment supports reduction of the current PQL"
category.
When the analysis of PT and PE data did not provide conclusive indications regarding whether
there was potential to revise a PQL, EPA reviewed two other sources of information. The first
source was the MRLs in the SYR3 ICR database (USEPA, 2016a). An MRL is the lowest level
or contaminant concentration that a laboratory can reliably achieve within specified limits of
precision and accuracy under routine laboratory operating conditions using a given method
(USEPA, 2016b). Through the SYR3 ICR, EPA received voluntary submissions of compliance
monitoring data for public water systems (PWSs) from 54 states and entities. The data contain a
large number of analytical non-detection records with accompanying MRLs for regulated
contaminants (see Section 3.7.1). When appropriate, EPA evaluated the distribution of MRL
values for contaminants to identify the mode, or value occurring most frequently for that
contaminant ("modal MRL"). The use of modal MRLs to provide additional insight into whether
there is potential to revise a PQL is another refinement of the protocol, necessitated by limited
3-15
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
availability of PT and PE data below the current PQL and made possible by the extensive
amount of information included in the ICR database.
The second type of information that EPA reviewed to evaluate the potential for a change in the
PQL was the MDLs for analytical methods approved by EPA for drinking water. In using MDLs,
EPA followed the multiplier approach used to derive some PQLs. This approach was also used to
identify possible analytical feasibility levels for the Six-Year Review 1 (USEPA, 2003b) and the
Six-Year Review 2 (USEPA, 2009). Based on these MDL values, EPA used an MDL multiplier
to estimate where the possible lower limit of quantitation may currently lie. The multiplier is 10
for most contaminants; the exception is contaminants for which EPA developed a PQL using a
multiplier of 5 (e.g., dioxin).
EPA also used the modal MRL and MDL-based estimates when it derived estimated quantitation
levels (EQLs) for the occurrence analysis to help the Agency determine if there was a
meaningful opportunity for health risk reduction. The EQL does not, however, represent the
Agency's intent to calculate new PQL at this time. Because of lack of data, EPA did not
recalculate PQLs during the Six-Year Review 2 or the Six-Year Review 3.
3.6.2 Output from Methods Review
The output of the Methods Branch is a decision regarding whether new information or
information from an earlier cycle indicates a potential to lower the PQL for a contaminant. The
decision tree then returns the review to the MCL Branch for subsequent questions.
3.7 Occurrence Branch
The purpose of the Occurrence Branch (Exhibit 3.7) is to determine if there is a potential
meaningful opportunity to revise an MCL by:
• Estimating the number of PWSs in which contaminants occur at levels of interest based on
health effects or analytical methods information, and
• Evaluating the number of people potentially exposed to these levels.
This occurrence and exposure information indicates how changing an MCL may affect health
risks and compliance costs.
3-16
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.7 Occurrence Branch
Are new monitoring
data available by
December 2015?
Can the data provide
occurrence estimates at
alternative MCLs
Are there SYR2
occurrence data
for alternative
MCLs?
Data gap
prevents
analysis
Estimate
affected
systems and
opulatio
Use SYR2
occurrence
data
Would MCL revision
provide a
meaningful
opportunity for
health risk or cost
reduction?
Return to source
(MCL 1orMCL2)
Key:
b Nn
Yes
3.7.1 Inputs to Occurrence Review
The initial questions elicit information regarding the availability of monitoring data for
estimating occurrence at alternate benchmarks (e.g., MCLs and EQLs). For the Six-Year Review
3, the responses to these questions reflected new data that EPA received through its Six-Year
Review ICR. EPA issued the ICR as a one-time voluntary request for states to submit historical
monitoring data (covering the years 2006 through 2011) for regulated contaminants to EPA. A
total of 54 states and entities provided compliance monitoring data that included all analytical
detection and non-detection records. These data represent the national occurrence of regulated
contaminants in public drinking water systems. If new monitoring data were not available from
the latest ICR data request, EPA would have reviewed monitoring data from the previous Six-
Year Review, in this case SYR2.
3-17
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Similar to the Six-Year Review 2 protocol, EPA also reviewed information on potential source
water quality for the contaminants with possible MCLG increases. Because the ICR data
represent water quality at entry points to the distribution system, the typical ICR occurrence
analysis results were not adequate to evaluate the cost savings potential for contaminants with
the potential for higher MCLG values. Therefore, EPA also evaluated source water quality
information for these contaminants. This information came from two national data sources: the
National Water Quality Assessment program conducted by the U.S. Geological Survey, and
EPA's STORET (short for STOrage and RETrieval) data system, which are part of OGWDW's
National Contaminant Occurrence Database.
Regardless of the occurrence data source and analysis method, EPA must determine whether the
extent of occurrence represents a meaningful opportunity to reduce health risks or costs; there is
no single benchmark for making this determination. The EPA Administrator has the discretion to
determine which revisions are appropriate, and may consider a variety of factors. These factors
include but are not limited to the type of health effects on the general population and sensitive
populations and life stages, including children; the geographical distribution of the affected
systems and populations; the size of the affected populations; and competing agency priorities
and resource constraints.
3.7.2 Output from Occurrence Review
The output of the Occurrence Branch is the identification of contaminants for which MCL
revision would provide a meaningful opportunity for health risk reduction or cost savings, while
maintaining or improving the level of public health protection. An additional result is the
identification of contaminants for which data gaps prevent an occurrence review. The decision
tree then returns the review to the MCL Branch for subsequent questions.
3.8 Treatment Branch
When EPA promulgates an MCL, the NPDWR also contains BAT recommendations for
drinking water treatment processes. To be a BAT, the treatment technology must meet several
criteria such as having demonstrated consistent removal of the target contaminant under field
conditions. Although treatment feasibility and analytical feasibility together address the technical
feasibility requirement for an MCL, historically, treatment feasibility has not been a limiting
factor for MCLs. Thus, the purpose of the Treatment Branch (Exhibit 3.8) is to ascertain that
there are technologies that meet BAT criteria when an MCL can be lowered, and doing so
presents a meaningful opportunity to reduce health risks.
3-18
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.8 Treatment Branch
Can BATs and SSCTs meet
alternative MCLs?
Can new
technologies
identified by
December 2015
meet alternative
MCLs?
Can achieve revised
MCL
Identify
potential
BATs and
SSCTs
Cannot achieve
revised MCL
Return to source
(MCL 1 or MCL 2)
¥¦ Yes
3-19
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
3.8.1 Inputs to Treatment Review
The Treatment Branch includes the following questions:
• Can the BATs and small system compliance technologies (SSCTs) meet alternative MCLs?
• Can new technologies identified by the cutoff date (December 2015) meet alternative MCLs?
For the Six-Year Review 3, EPA limited its review of BATs to those NPDWRs for which it was
considering possible revisions to the MCL based on the health effects or analytical feasibility
reviews. To address both questions, EPA conducted a review of treatment performance studies
for all applicable technologies for the contaminant in question. EPA used the same sources that it
has relied on in the past to develop regulations and guidance, including published EPA treatment
reports, peer-reviewed journals and other sources of technology performance (e.g., pilot and
demonstration project reports), as well as information received from EPA stakeholders. EPA
evaluated whether these treatment studies indicate that current BATs are capable of achieving
possibly lower MCLs and whether newer treatment technologies potentially meet BAT criteria.
3.8.2 Output of Treatment Review
The output of the Treatment Branch is a determination of whether treatment feasibility would
pose a limitation to revising an MCL. The decision tree then returns the review to one of the
MCL Branches for subsequent questions.
3.9 Risk-Balancing Branch
The Risk-Balancing Branch (Exhibit 3.9) is applicable only to the review of the MDBP rules,
which were promulgated to address balancing between microbial and DBP requirements, and
among differing types of DBPs. This effort was based on the SDWA requirement that EPA
"minimize the overall risk of adverse health effects by balancing the risk from the contaminant
and the risk from other contaminants the concentration of which may be affected by the use of a
treatment technique or process that would be employed to attain the maximum contaminant
level."
The purpose of the Risk-Balancing Branch is to identify how the Six-Year Review addresses
tradeoffs in risks for regulated and unregulated contaminants. Under this branch, EPA considers
whether a change to an MCL and/or TT will affect the risk from one or more other contaminants,
and, if so, considers revisions that will balance these overall risks. This approach was used in the
development of several NPDWRs, such as those for the Long-Term 2 Enhanced Surface Water
Treatment Rule and the Stage 2 D/DBPR, promulgated in January 2006.
3.9.1 Inputs to Risk-Balancing Branch
The Risk-Balancing Branch includes the following question:
• Could the change to an NPDWR affect the risk from one or more contaminants, and, if so,
will the change increase the risks of adverse health effects from that contaminant?
3-20
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
For the Six-Year Review 3, EPA reviewed risk-balancing between microbial and DBP
contaminants. For example, EPA considered the potential impact on DBP concentrations should
there be a consideration to increase the stringency of microbial protection rules. In addition, EPA
reviewed risk-balancing between different types of DBP contaminants. Depending on the
stringency of potential DBP regulations, there may be response strategies used by the regulated
community that might have the effect of increasing the concentrations of other types of
contaminants (regulated and unregulated). EPA considered these potential response strategies,
with a goal of balancing the overall risks.
3.9.2 Outputs from Risk-Balancing Branch
The output of the Risk-Balancing Branch is a determination of whether additional revisions to
the MCL and/or TT are needed to help balance the overall risks from potential changes.
Following this determination, the decision tree then transitions to the Implementation Branch for
subsequent questions.
Exhibit 3.9 Risk-Balancing Branch
Consider
revisions to the
MCL and/or TT
that will balance
the overall risks
/ Takeno\
further action
on revised
MCL and/or
Could the MCL and/or
TT change?
GO TO
Implementation
Branch
Is the contaminant a
microbial, disinfectant,
or DBP contaminant?
Could the change
affect the risk from
one or more other
contaminants?*
Will the change
increase the risk of
adverse health effects
from that contaminant?
Key:
Yes
includes microbial contaminants and DBPs (regulated and unregulated).
3.10 Implementation Branch
The purpose of the Implementation Branch (Exhibit 3.10) is to evaluate potential revisions
pertaining to "other" regulatory requirements, such as monitoring and system reporting.
Regulatory revisions to MCLs or TTs may affect the monitoring and system reporting
requirements for a contaminant and new health risk information may also warrant revisions.
3-21
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
Exhibit 3.10 Implementation Branch
Consider
revisions
Take no action
on other
implementation
\ issues /
End
Is a revision to the
MCLorTT
warranted?
Will it affect
monitoring/reporting
requirements?
Key:
Yes
Will the change
affect
monitoring/reporting
requirements?
Is there new health
risk information on
reproductive or
developmental
toxicity?
3.10.1 Inputs to Implementation Review
The Implementation Branch requires information regarding whether a change in a contaminant's
MCL or TT or new health effects information will affect the monitoring and system reporting
requirements for a particular contaminant. For the Six-Year Review 3, EPA focused this review
on issues that were not already being addressed through alternative mechanisms, such as through
a recent or ongoing rulemaking. EPA also reviewed implementation-related NPDWR concerns
that were "ready" for rulemaking - that is, the problem to be resolved had been clearly identified,
along with specific options to address the problem, and shown to either clearly improve the level
of public health protection, or represent a meaningful opportunity for cost savings while
maintaining the same level of public health protection.
3.10.2 Outputs from Implementation Review
The output of the Implementation Branch is a determination regarding whether EPA should
consider revisions to the monitoring and system reporting requirements of an NPDWR. It is the
final branch of the decision tree.
3-22
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
4 References
USEPA. 1985. National Primary Drinking Water Regulations: Volatile Synthetic Organic
Chemicals; Final Rule and Proposed Rule. 50 FR 46880. November 13, 1985.
USEPA. 1986. Guidelines for Carcinogen Risk Assessment. EPA 630-R-00-004. September
1986. Available online at: http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockev=30004TZX.txt
USEPA. 1987. National Primary Drinking Water Regulations-Synthetic Organic Chemicals;
Monitoring for Unregulated Contaminants; Final Rule. 52 FR 25690. July 8, 1987.
USEPA. 1989. National Primary and Secondary Drinking Water Regulations: Proposed Rule. 54
FR 22062. May 22, 1989.
USEPA. 1999. Guidelines for Carcinogen Risk Assessment Review draft. NCEA-F-0644. July
1999. Available online at: http://nepis.epa.gov/Exe/ZvPURL.cgi?Dockev=500022VK.txt
USEPA. 2003a. National Primary Drinking Water Regulations; Announcement of Completion of
EPA's Review of Existing Drinking Water Standards; Notice. 68 FR 42908. July 18, 2003.
USEPA. 2003b. EPA Protocol for Review of Existing National Primary Drinking Water
Regulations. Washington, DC: Office of Ground Water and Drinking Water. EPA 815-R-03-002.
June 2003. Available online at:
http://nepis.epa.gov/Exe/ZvPDF.cgi/20001ZLT. PDF? Dockev=20001ZLT. PDF
USEPA. 2005. Guidelines for Carcinogen Risk Assessment EPA/630/P-03/001F. March 2005.
Available online at: https://vvvvvv.epa.gov/risk/guidelines-carcinogen-risk-assessment
USEPA. 2009. EPA Protocol for the Second Review of Existing National Primary Drinking
Water Regulations (Updated). Washington, DC: Office of Ground Water and Drinking Water.
EPA 815-B-09-002. October 2009. Available online at:
https://vvvvvv.epa.gov/sites/production/files/2014-12/documents/815b09002.pdf
USEPA. 2010. National Primary Drinking Water Regulations; Announcement of the Results of
EPA's Review of Existing Drinking Water Standards and Request for Public Comment and/or
Information on Related Issues. 75 FR 15500. March 29, 2010.
USEPA. 2015. Science Policy Council Handbook: Peer Review, 4th Edition. Washington, DC.
EPA 100-B-15-001. October 2015. Available online at:
https://vvvvvv.epa. gov/ sites/production/files/2016-
03/documents/epa peer review handbook 4th edition.pdf
USEPA 2016a. Six-Year Review 3 ICR Database.
USEPA. 2016b. Analytical Feasibility Support Document for the Third Six-Year Review of
National Primary Drinking Water Regulations: Chemical Phase Rule and Radionuclides Rules.
EPA-810-R-16-005.
4-1
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
USEPA. 2016c. Chemical Contaminant Summaries for the Third Six-Year Review of Existing
National Primary Drinking Water Regulations. EPA-810-R-16-004.
USEPA. 2016d. Consideration of Other Regulatory Revisions in Support of the Third Six-Year
Review of the National Primary Drinking Water Regulations: Chemical Phase Rules and
Radionuclides Rules. EPA-810-R-16-003.
USEPA. 2016e. Development of Estimated Quantitation Levels for the Third Six-Year Review
of National Primary Drinking Water Regulations (Chemical Phase Rules). EPA-810-R-16-002.
USEPA. 2016f. Occurrence Analysis for Potential Source Waters for the Third Six-Year Review
of National Primary Drinking Water Regulations. EPA-810-R-16-008.
USEPA 2016g. Six-Year Review 3-Health Effects Assessment for Existing Chemical and
Radionuclide National Primary Drinking Water Regulations-Summary Report.
USEPA. 2016h. Occurrence Data for the Unregulated Contaminant Monitoring Rule- July 2016.
USEPA. 2016i. Six-Year Review 3 Technical Support Document for Chlorate. EPA-810-R-16-
013.
USEPA. 2016j. Six-Year Review 3 Technical Support Document for Disinfectants/Disinfection
Byproducts Rules. EPA-810-R-16-012.
USEPA. 2016k. Six-Year Review 3 Technical Support Document for Long- Term 2 Enhanced
Surface Water Treatment Rule. EPA-810-R-16-011.
USEPA. 20161. Six-Year Review 3 Technical Support Document for Microbial Contaminant
Regulations. EPA-810-R16-010.
USEPA. 2016m. Six-Year Review 3 Technical Support Document for Nitrosamines. EPA-810-
R-16-009.
USEPA. 2016n. The Analysis of Regulated Contaminant Occurrence Data from Public Water
Systems in Support of the Third Six-Year Review of National Primary Drinking Water
Regulations: Chemical Phase Rules and Radionuclides Rules. EPA-810-R-16-014.
USEPA. 2016o. The Data Management and Quality Assurance/Quality Control Process for the
Third Six-Year Review Information Collection Rule Dataset. EPA-810-R-16-015.
USEPA. 2016p. Spring 2016 Regulatory Agenda. 81 FR 37377. June 9, 2016.
USEPA. 2016q. Technologies for Legionella Control in Premise Plumbing Systems: Scientific
Literature Review. EPA 810-R-16-001.
4-2
-------
EPA-OGWDW EPA Protocol for the Third Review of Existing EPA 810-R-16-007
National Primary Drinking Water Regulations December 2016
USEPA. 2016r. Support Document for Third Six-Year Review of Drinking Water Regulations
for Acrylamide and Epichlorohydrin. EPA 810-R-16-019.
4-3
------- |